The diagnosis of diseases through analysis of human breath has long been practiced in medicine. For example, by smell alone, various volatile components of breath such as acetone, ammonia or sulfur compounds can be detected and provide information used to evaluate conditions such as diabetes, liver impairment and kidney dysfunction. Gas chromatography and mass spectrometry also have been applied to evaluate exposure to toxic substances, liver disease and lung cancer.
Thus, the measurement of exhaled substances may be useful as a diagnostic and prognostic tool for a wide variety of medical conditions. Often, it is of interest when assessing pulmonary function to measure one or more of a variety of exhaled substances. These include endogenous gases (i.e., oxygen, carbon dioxide and nitric oxide), exogenous gases used to test pulmonary diffusing capacity (i.e., carbon monoxide, acetylene, argon and helium), volatile substances (i.e., ethane and pentane) and non-volatile substances (i.e., proteins such as surfactants, DNA and hydrogen peroxide) often found by sampling the liquid present in exhaled breath (i.e., breath condensate).
One exhaled substance of particular interest is exhaled endogenous nitric oxide (“NO”). Nitric oxide is now known to be a central mediator in biological systems and, therefore, endogenous exhaled nitric oxide is thus potentially of interest in the diagnosis and monitoring of pulmonary function and various pulmonary diseases. Nitric oxide can be measured in the exhaled breath of animal and human subjects and shows particular promise as a diagnostic tool useful in evaluating inflammatory airway diseases, in particular bronchial asthma, and also in evaluating bronchiectasis and lung transplant rejection and other pulmonary conditions.
For example, asthmatic patients have relatively high exhaled NO levels as compared to normal subjects and these levels decrease rapidly after the institution of anti-inflammatory therapy. Thus, measuring exhaled NO in conjunction with existing tests may aid in the diagnosis and assessment of asthma, and also be an index of the response to therapy, or patient compliance in therapy. In view of the importance of asthma as a major health problem, the commercial potential is great for tests that can help diagnose asthma severity and ascertain the response to therapy.